Lint Quality Research Articles

Lint development and properties of fifteen fuzzless seed lines of Upland cotton (Gossypium hirsutum L.)

Fifteen fuzzless seed lines in “obsolete” backgrounds of Upland cotton (Gossypium hirsutum L.) were obtained from the National Cotton Germplasm Collection and evaluated for fuzzless seed genotype, lint percent, and lint quality. Fourteen of these fifteen lines were found to be homozygous for the dominant fuzzless seed allele N 1. Only one line was homozygous for the recessive fuzzless seed allele n 2. The measured lint percent of each line was very stable through time, however, large variability existed between many of the N 1 lines ranging from 0.7 to 23.6% lint. The lint percent for the n 2 line was 24.4%. Scanning electron microscopy was used to differentiate patterns of lint initiation on 1 day post anthesis ovules. General patterns included: first, lint initiation restricted to the chalazal end of the seed crest; second, lint initiation along the seed crest and laterally around the chalazal end of the ovule; and third, lint initiation covered all but the micropylar end of the ovule. Lint quality was evaluated for each line using the Advanced Fiber Information System (AFIS) which included measurements of length, maturity, and fineness. The means of each measurement varied among the fuzzless seed lines with significant differences between fiber length, short fiber content, immature fiber content, fineness, and maturity ratio. No correlation was found between lint percent and any of the lint quality measurements. These lines will provide a valuable resource for the study of fiber initiation and lint quality.

Adult attractiveness and oviposition preference of Bemisia tabaci (Genn.) (Homoptera: Aleyrodidae) B-biotype in cotton genotypes

The silverleaf whitefly Bemisia tabaci B-biotype is an important pest of cotton; it affects plant vigour, transmits geminivirus and reduces lint quality. In order to evaluate the resistance of cotton genotypes, Gossypium hirsutum (L.), to the whitefly Bemisia tabaci B-biotype, both free-choice and no-choice attractiveness and non-preference for oviposition tests were carried out in a shade house, at room temperature. Low attractiveness to adults of this whitefly was observed for plants of genotypes Fabrika, CNPA Ita 90, Makina, Coodetec 407, and IAC 01-639 CPA 02-24, which may represent a resistance component of these genetic materials to the insect. Genotypes BRS Aroeira, Coodetec 406, Fabrika, and Coodetec 401 presented the non-preference-for-oviposition type of resistance in the free-choice and no-choice tests. The numbers of trichomes and gossypol glands per cm² were not suitable to evaluate non-preference for oviposition of whitefly adults on cotton genotypes.

Improving the Conservation and Effectiveness of Arthropod Parasitoids for Cotton Pest Management

Cotton is infested by sucking pests (aphids, jassids, whiteflies, thrips, plant bugs) and bollworms causing deterioration in lint quality and 10–40% losses in crop production. Insecticides used extensively to control these pests cause undesirable secondary effects including the destruction of arthropod parasitoids, which constitute an important component of pest management. When released parasitoids die or become ineffective in cotton ecosystems, the classical biological control fails. Therefore, conservation of potential parasitoids is nowadays considered a major step in maintaining populations in a region where they could reduce the pest population density below economic thresholds and reduce plant damage below economic injury levels. By employing the least disruptive control measures and by adopting proper habitat management, it would be possible to enhance the survival, conservation and physiological/behavioural performance of the generalist and specific parasitoids in cotton-production systems.

Biological contamination parameters of cotton lint as biomarkers for fibre quality; a preliminary study

It has been reported for several decades that microbes, which naturally contaminate cotton fibres during crop growth and subsequent storage can have an adverse effect on the structural quality of cotton lint. Although several studies have analysed the relationship between numbers of Gram-negative bacteria or bacterial endotoxin and particular physical properties, these studies have been limited to cotton from the United States, and the possible effects of fungal contamination have not been examined in detail. This study quantified the Gram-negative bacteria and fungal cells, as well as measuring concentrations of bacterial endotoxin and fungal glucan, on cotton lint samples from international sources. Spearman’s rank correlation coefficients calculated between these results and quality data analysed by an automated testing instrument revealed several significant correlations. Findings included inverse correlations between the biological contamination parameters and fibre elongation, micronaire and reflectance. The possible causes and implications of these findings were also discussed.

EFFECT OF FOLIAR APPLICATION OF POTASSIUM ON LINT YIELD AND LINT QUALITY OF COTTON

A field experiment was conducted at the IPA Field Crops Research Station, Abu – Graib during 2002 season and at Experimental Field, Department of Field Crop Science, College of Agricultur , Abu – Graib during 2004 season. The objective of this research was to study the effect of six levels of foliar potassium application 500 ppm at start of flowering and 500 ppm at start of boll development, 1000 ppm at start of flowering and 1000 ppm at start of boll development, 1500 ppm at start of flowering and 1500 ppm at start of boll development, 2000 ppm at start of flowering and 2000 ppm at start of boll development, 2500 ppm at start of flowering and 2500 ppm at start of boll development, 3000 ppm at start of flowering and 3000 ppm at start of boll development in additional to control treatment (without spray) on seed cotton yield, lint yield and lint quality of cotton var. Cocker 310. A randomized complete block design was used with three replications. The results indicated that highest response of Cocker 310 c.v . to increasing potassium foliar application was by 3000 ppm at start of flowering and 3000 ppm at start of boll development, it gave asignificant increasing in the number of sympodia, number of open bolls, boll weight, seed cotton yield, dry matter ,lint yield and fiber strength as compared to control in both seasons. While seed , number/boll, fiber length and fiber fineness did not significantly affected by all the level of potassium applied on the two season.

Response of cotton ( Gossypium hirsutum L.) to different tillage systems and intra-row spacing

The earliness is of great importance to cotton production in Mediterranean-type environments due to detrimental effects of autumn rainfall on lint quality. However, farmers commonly avoid early sowing due to risks of cold soil temperature and waterlogging after sowing in spring. Ridge-tillage system is one approach to increase soil temperature and mitigate adverse effects of waterlogging. The ridge-tillage system is also advantageous in reducing inputs in tillage operations. However, a limited experimental data are available about the effects of ridge-tillage system on earliness of harvesting, lint yield and quality of cotton in the Mediterranean-type environments. Thus, the objective of this study was to determine how ridge-tillage (RT)-planting system and intra-row spacing affect cotton lint yield, earliness and fiber quality compared with conventional tillage (CT)-planting system. Field experiments were conducted on a clay soil (Vertisol) in Hatay province (36°39′N–36°40′E, 83 m a.s.l.) in the Eastern Mediterranean Region of Turkey during 2000 and 2001. The experiment was laid out as a split-plot with three replications with tillage systems as main plots and intra-row spacings (13, 17, 21 and 25 cm) as subplots. The effects of tillage systems on lint yield and earliness were inconsistent among years. The RT-planting system resulted in 13.5% higher lint yield and 14.5% more earliness in 2001 when abundant rainfall occurred after sowing, while significant effects of tillage systems were not observed in 2000. The intra-row spacings significantly affected lint yield and earliness in both years. The earliness increased with closer spacing, while the highest lint yield was obtained from 17 cm intra-row spacing in both years. However, the fiber quality parameters were not significantly affected by tillage systems, intra-row spacings and tillage system × spacing interaction in both years. Finally, the results suggest that RT-planting system with 17 cm intra-row spacing can be used in cotton production instead of CT-planting system in the Eastern Mediterranean Region of Turkey. Ridging in 17 cm intra-row spacing also seems to be suitable to mechanical harvesting.

MAPPING PHYMATOTRICHUM ROOT ROT OF COTTON USING AIRBORNE THREE-BAND DIGITAL IMAGERY

Phymatotrichum root rot, caused by the fungus Phymatotrichum omnivorum, is a serious and destructive diseasethat significantly reduces cotton yield and lowers lint quality. Cultural practices are commonly recommended for the controlof cotton root rot, and fungicides and fumigants that may suppress the disease have also been used. Because of the high costsof these chemicals, their use may be economically feasible only when the infested portions of the field are treated. Theobjective of this study was to evaluate airborne multispectral imagery for detecting and mapping root rot areas in cotton fieldsfor site-specific management of the disease. One center-pivot irrigated field and one rainfed field near Corpus Christi, Texas,were selected for this study. Airborne three-band digital imagery was taken from the two fields shortly before harvest in 2001when the infested areas with wilted and dead plants were almost fully pronounced for the season. The imagery wasgeoreferenced and then classified into healthy and root rot areas using unsupervised classification. Accuracy assessment onthe classification maps for the two fields indicated that airborne imagery effectively and accurately identified root rot areaswithin the fields. Ground samples taken from the fields showed that cotton yield and some lint quality indices were significantlylower in root rot areas than in healthy areas. Buffer zones around the root rot areas were generated to account for the spreadof cotton root rot on the classification maps. The mapping procedures and maps presented in this study will be useful forsite-specific management of the disease.

Cotton Response to Source and Timing of Nitrogen Fertilization on a Sandy Coastal Plain Soil

A three‐year field study was conducted to evaluate cotton (Gossypium hirsutum L.) response to the source and timing of nitrogen (N) on an irrigated coastal plain soil (Lucy loamy sand; Arenic Kandiudults) in south Alabama. Cotton acreage in this region has increased in the past ten years and there was a need for current data describing cotton response to N fertilization. Treatments included N sources, timing of N application (ammonium nitrate), split applications of N (ammonium nitrate and ammonium sulfate), and a no‐N check. Nitrogen sources applied preplant included: (i) ammonium nitrate (34‐0‐0); (ii) ammonium sulfate (21‐0‐0‐24.2); (iii) urea (46‐0‐0); (iv) urea–ammonium nitrate solution (UAN; 32‐0‐0); (v) UAN + ammonium thiosulfate (28‐0‐0‐5). Non‐sulfur sources were applied with and without additional sulfur (S). Times of application were preplant, first true leaf, first square, and first bloom. Two treatments received split applications of N as a 50:50 mixture of ammonium sulfate with urea or ammonium nitrate. Supplemental applications of potassium (K) were evaluated by applying ammonium sulfate in combination with 56 kg K/ha. Yield data showed some minor differences among sources, but overall the results of this three‐year study show that there were no superior N sources. For ammonium nitrate, preplant applications of N were sufficient in two out of three years. Split applications of ammonium nitrate did not improve yields as compared to preplant N. Applying ammonium sulfate with supplemental K or as a 50:50 mixture with ammonium nitrate or urea did not improve yields as compared to ammonium sulfate or ammonium nitrate applied alone. Lint quality was not affected by N fertility treatments.

Effects of Quality Considerations and Climate/Weather Information on the Management and Profitability of Cotton Production in the Texas High Plains

Production function models for cotton lint yields, seed yields, turnout, and lint quality characteristics are developed for the Texas High Plains. They are used to evaluate the impacts of quality considerations and of climate/weather information on the management decisions and on the profitability and risk of irrigated cotton production systems. It is concluded that both quality considerations and improved climatic/weather information could have substantial effects on expected profitability and risk. These effects mainly occur because of changes in optimal variety selection and irrigation water use levels. Quality considerations in particular result in significantly lower irrigation water use levels regardless of the climate/weather information assumption, which has important scarce-resource use implications for the Texas High Plains.

Developing management options for mepiquat chloride in tropical winter season cotton

Little research had been conducted on managing cotton growth using mepiquat chloride (MC) during the tropical winter season. Three experiments were conducted over three seasons. Early season internodes (first nine nodes) were long compared to temperate climates. Consequently the effect of MC applied, as multiple or single doses, from four nodes to first flower was evaluated. MC dramatically reduced height and node number in proportion to a total amount of MC up to 45 g/ha, r 2=0.66 and r 2=0.81, respectively; this response was independent of the frequency of treatment. Lint yields were high averaging 2143, 2415 and 2312 kg/ha for the three seasons. Despite the number of fruiting branches declining linearly with the amount of MC lint yields were decreased ( p<0.05) in only 2 of the 28 treatments. There was a trend to increased yield (106.5%) compared with untreated plants where between 9 and 18 g/ha MC was intercepted. There was no economic effect of MC on lint quality. Yield compensation for reduced fruiting branches due to MC was via a linear increase in boll retention over all fruiting sites and vegetative branch bolls, which peaked with 35 g/ha of MC for each yield component. Where >35 g/ha was intercepted yields were the same or reduced compared to untreated plants. Compensation via boll size, possibly related to position, was implicated in this yield response. Thus treatment with 9–18 g/ha of MC, between 4 and 11 nodes, provided a compromise between suppressing plant height for operational efficiency, and optimising these yield components. Crop monitoring techniques based on the length of internodes could not aid MC treatment decisions because critical lengths, developed for temperate locations, were always exceeded and there was rarely a yield response to MC. An explanation came from the independence to MC of the height-to-nodes ratio prior to flowering. Monitoring techniques based on predicting the height and node number response from the MC concentration within the plant showed promise. MC did not affect time to maturity despite ≤15-day reduction in main-stem flowering period due to MC. This difference was attributed to high and increasing end-of-season temperatures synchronising maturity in bolls from later flowers, and it was possible vegetative branch bolls, increased by MC, matured after main-stem bolls. It was suggested future research consider modelling the MC response, irrigation interactions, the cultivar response, the effect on duration of flowering, and the interaction between MC and yield compensation from insect damage.

LINT QUALITY AND TURNOUT OF STRIPPER COTTON WHEN BYPASSING THE SECOND STAGE EXTRACTOR

Equipment such as stick machines, bur machines, extractorfeeders, and combination bur and stick machines havecommonly been referred to as extractingtype machinery or extractors. Extractors provide the capability of removing bursand sticks from seed cotton prior to ginning and are therefore an essential part of a cotton gins seed cotton cleaning system.Most cotton gins processing stripper cotton have more than one stage of extraction. The effect that bypassing the second stageof extraction has on turnout has not been studied to any considerable extent. Thus, the objective of this study was to investigatethe impact on turnout and fiber quality due to bypassing the second stage stick machine. Results indicate that bypassing thesecond extractor in the gins seed cotton cleaning system, when handling fieldcleaned cotton, did not significantly affectfiber properties or lint turnout. For nonfield cleaned cotton, however, the bypassing of the second stage extraction adverselyaffected Rd color (reflectance), HVI trash area, leaf grade, and AFIS dust concentration after one lint cleaner. Bypassing thesecond extractor also significantly increased the total lint cleaner waste for both field cleaned and nonfield cleaned cottons.However, the amount of lint lost throughout the system was unaffected. Overall, the effect of the second stage extractors onturnout and lint quality can vary depending on the machine design, condition, feed rate, and on the nature of the cotton itself.However, in this study, bypassing the second stage of extraction did not significantly affect turnout when processing eitherfield cleaned or nonfield cleaned cotton.

VARIABILITY OF COTTON YIELD AND QUALITY

Precision agriculture technologies offer an opportunity to vary production inputs within a field. Variable rate application offers the potential to increase production efficiency and minimize potential adverse environmental effects of agricultural chemicals. As an initial step in the development of precision agriculture technologies for cotton, studies are needed to document variability of cotton. The primary objective of this study was to document variability of yield and quality of irrigated cotton within and across three growing seasons. This study was conducted on a 5.3 ha irrigated field located at the Erskine Research Farm at Texas Tech University, Lubbock, TX. The crop was grown under a conventional tillage system with a 1.0 m row spacing. With the exception of sample collection, the field was managed traditionally with respect to production inputs. A grid system (57 points) was established on 30.5 m (approximately 0.1 ha) intervals. Production of fruiting sites, fruit retention, lint yield, fiber length, strength, micronaire, and gross revenue were estimated for each grid point. Soil chemical and physical properties were also determined for each grid point. Highest variability was observed for lint yield and production of fruiting sites, and lowest variability was observed for lint quality parameters. Yield was correlated to production of fruiting sites each season. Nitrate concentrations were highly variable, and yield was negatively correlated to nitrogen (N) in 1997. This suggests that variable application of N may be a viable management option in the future. Yield was positively correlated to calcium (Ca), pH, and CEC in 1997. Yield variability was correlated across growing seasons. Gross revenues were quite variable, due primarily to yield variability.

Comparative efficiency of honeycomb and conventional pedigree methods of selection for yield and fiber quality in cotton (Gossypium spp.)

The effectiveness of honeycomb pedigree selection (HPS) as compared to conventional pedigree selection (CPS) was studied in one intraspecific (G. hirsutum L. × G. hirsutum L.) cross population (population I) and one interspecific (G. hirsutum L. × G. barbadense L.) cross population (population II). Combined selection for yield and lint quality traits was applied for four cycles at two locations for population I and atone location for population II. Finally, the best F6 lines derived by each method, together with the unselected population derived by single seed descent (SSD) and three check cultivars, were tested in comparative experiments, separately for each cross, at the same locations. In both populations the analysis of variance indicated significant differences among the groups of the material tested for seed cotton yield, mean boll weight, micronaire reading, staple length, and uniformity ratio. No significant differences were found with respect to plant height, lint percentage, and fiber strength in population I and with respect to lint percentage and fiber strength in population II. In population I, on the basis of mean seed cottonyield and number of superior lines derived by each method as compared to the check varieties and the unselected SSD population, HPS-lines were superior to CPS-lines for seedcotton yield, fiber length and boll weight. HPS-lines, however, did not differ significantly in seedcotton yield from the best check cultivar Eva. Finally, the material derived by CPS was earlier in maturity than the material derived by HPS and SSD. Also in population II, on the basis of mean seedcotton yield and number of superior lines derived by each method as compared to the unselected SSD population, HPS-lines were superior to CPS-lines. No significant differences, however, were identified between the material of the two methods for lint quality traits. It was concluded that in both populations HPS was more effective than CPS in identifying lines with high yielding ability and good lint quality. This superiority of HPS is attributed, at least partially, to its effectiveness in early generation selection.

Physiological Parameters, Harvest Index and Yield of Deficient Irrigated Cotton

Summary The agronomic and physiological response of cotton to deficient irrigation as well as its influence on yield quality was determined. Plant growth expressed as plant height and accumulation of fresh weight was significantly affected by water deficit. Nevertheless, neither seed cotton yield nor lint quality were decreased. Turgor pressure was maintained positive for the entire growth cycle. The relationship between growth and yield parameters is discussed.

The trade-off between economic efficiency and food self-sufficiency in using Sudan's irrigated land resources

A shift in Sudan's food production strategy towards more reliance on the irrigated sector for food supply has been induced by the severe food shortages following the early 1980s drought and reduced availability of food aid. Coupled with the high yield potential of irrigated wheat under modern technology revealed by recent research results, this led to significant expansions in the areas of irrigated food crops, especially wheat after 1989. This paper used domestic resource cost analysis to examine whether the expansion in irrigated wheat production represents the most efficient option for using Sudan's irrigated land resources as compared to cotton, the country's most important cash crop competitor. At the 1993 prices, medium-staple cotton dominated various wheat technologies in terms of economic efficiency. An efficiency frontier was constructed to evaluate the sensitivity of competitiveness results to changes in productivity gains and price shifts. Wheat yields currently achieved by average farmers on the scheme need to increase by more than 50% for wheat to compete with cotton at the 1996 prices. In other words, currently one ha of exported cotton generates economic returns that are sufficient to import about 50% more wheat than can be domestically produced from the same ha under average farmers' practices in Gezira. In addition to its superiority over wheat in economic efficiency terms, cotton has larger employment benefits than wheat, being the more labour intensive enterprise. This means that expanding irrigated wheat production in Gezira for food self-sufficiency at the expense of cotton reduces employment opportunities in addition to compromising economic efficiency. Priority should therefore be given to increased investment in research on improving cotton production technology, marketing and lint quality. On the other hand, it is important to introduce more effective policy measures for faster adoption of improved wheat technologies to close the gap between potential and current yield levels.

Preliminary studies show yield and quality potential of organic cotton

For three years (1993 to 1995), we monitored organically and conventionally managed cotton fields in Madera County, and measured pest and beneficial arthropod populations, plant growth and development parameters, nutrient status, plant density, yields and lint quality. Square (flower bud) retention was similar in the two systems, although western tarnished plant bugs (Lygus hesperus or lygus bugs) were significantly more abundant on several dates in the organic fields. On most dates, populations of the predatory insects Geocoris spp. were significantly higher in the organic than in the conventional fields. Lint yields were not significantly different for the two production systems in any of the three years, but were lower than county averages in all years. In 1994, lint quality in the two treatments differed in that color grades were more variable in the organic cotton bales. Late spring rains also affected planting success in each year and the shortened seasons in 1994 and 1995 generally kept yields in both treatments at or below two bales per acre.

Cotton Response to Surface Applications of Potassium Fertilizer: A 10-Year Summary

Field studies were conducted for 10 yr on a Limestone Valley soil (Dewey silt loam, a fine, kaolinitic, thermic Typic Paleudults) in north Alabama to evaluate cotton (Gossypium hirsutum L.) yield and lint quality response to long-term surface applications of K. Potassium rates were 0, 60, 120, and 180 lb K 2 O/acre for the first 3 yr of the study. Fertilizer was broadcast in the spring or split applied in fall and spring. No K fertilizer was applied during the fourth year (1990). After the fourth year, half of the treatments were left in residual and remaining treatments continued to receive annual applications of K (1991-1996). The experiment was a split plot arrangement of a randomized complete block. From 1987 to 1989, two varieties were compared, which served as whole plots. From 1991 through 1996, one variety was grown and annual vs. residual K fertilization served as whole plots. Potassium treatments were used as subplots throughout the test. From 1987 to 1989 there were no differences between 'Stoneville 825' and 'Deltapine 50'. Lint yields were increased significantly by K fertilization in 6 of 9 yr that cotton was grown on this low K soil. Potassium fertilization increased lint yields by as much as 450 lb/acre in responsive years. From 1991 through 1996, residual K produced lesser yields than where K was applied annually. There were no differences in lint yield among split (fall-spring), fall, or spring applied K. In responsive years, micronaire increased with K rate. Our results support the calibration currently used by the Auburn University Soil Testing Lab for Limestone Valley soils.

Performance of cotton F1 hybrids and its relation to the mean yield of advanced bulk generations

The performance of intraspecific (Gossypium hirsutum) and interspecific (G. hirsutum × G. barbadense) F1 cotton hybrids and its correlation with the mean yield of advanced bulk generations was assessed under Greek environmental conditions. For this, 14 intraspecific and five interspecific cotton F1 hybrids were evaluated at two locations (Sindos and Vardates) during the 1985–88 period. In addition, two interspecific hybrids (5, 6), the three best (8, 7, 11) and two among the worst (4, 10) intraspecific F1s and their F2 bulks were also evaluated at Sindos in 1986. This evaluation was repeated in the following years. In each successive year the new generation (up to the F5 bulk) was included.Intraspecific F1 hybrids outyielded the best variety at both locations. Lint yield of the F1 hybrids ranged from 99 to 158% with a mean value of 122%. Useful F1 heterosis (hybrids with higher values than the best check cultivar) was also expressed for boll weight and Verticillium wilt infestation. The latter was more pronounced in hybrids derived from tolerant parents.All F1 interspecific hybrids were dominated by the barbadense phenotype and had its superior fiber lint quality, lower lint percentage, and resistance to Verticillium wilt. In addition, they expressed positive heterosis for lint yield at Sindos and negative at Vardates, compared with the check variety. The frequency of the hirsutum phenotype progressively increased in the F2 through F5 generations, with plant height, boll weight, earliness, fiber quality and wilt tolerance moving toward the hirsutum values.In the F2 generation yield dropped dramatically (>50%) in the interspecific hybrids, whereas in the intraspecific hybrids inbreeding depression was much less and varied from hybrid to hybrid. The good F1s intraspecific hybrids maintained part of their useful heterosis in the F2. From the F3 onwards the yield improved in the interspecific crosses and stabilized around 75% of the yield recorded in the best check variety. In contrast, the highest yielding F1 intraspecific hybrids yielded progressively less in subsequent generations, and in the F5 they produced the same yield as the best cultivar, whereas the yield of the lowest yielding intraspecific hybrids was stabilized around 95% of the yield recorded in the best cultivar. It was concluded that yield of the F1 did not predict the yield of the bulks in the following generations. Yet, the combined performance of the hybrids in the F1 and F2 generation could be a good indicator to identify the most promising populations to be utilized either as F2 hybrids or as a source population for further selection.

Physiological changes associated with potassium deficiency in cotton

Potassium (K) fertility recommendations based on cotton petiole diagnostic analysis results have been inconsistent in the past, partly because the lowest acceptable petiole K concentration is unknown. Therefore, cotton was grown in sand filled 8‐L pots under two K treatments in a growth chamber at the Altheimer Laboratory in Fayetteville, AR to determine the petiole K concentration that will impact leaf physiology. Chamber‐grown plants were watered every second day with nutrient solution and with deionized water on alternate days. At 14 days after planting two treatments were established consisting of (1) continued complete nutrient solution, and (2) nutrient solution containing no K. Measurements were taken 13, 19, and 26 days after treatment establishment (DATE). Organ K concentrations, leaf chlorophyll, photosynthesis, adenosine triphosphate (ATP), and nonstructural carbohydrate concentrations were monitored as plant K deficiencies developed. All organ K concentrations were much lower in the no‐K treatment on each analysis date. Visual K deficiencies were first observed at 19 DATE along with reductions reductions in leaf chlorophyll concentration. Leaf photosynthesis was greatly reduced in the no‐K treatment beginning at 19 DATE. However, leaf ATP and nonstructural carbohydrate concentrations were higher at 19 and 26 DATE in the no‐K treatment, which may have been the result of reduced utilization and translocation of these metabolites. Our studies show that reductions in leaf physiological processes and plant growth did not occur until the petiole K concentration fell below 0.88% on a dry weight basis. Therefore, reductions in lint yield and quality should not develop until this critical petiole level is attained.

Action Thresholds for the Management of Bemisia tabaci (Homoptera: Aleyrodidae) in Cotton

A 2-yr, multistate project was initiated in 1994 to determine action thresholds for management of Bemisia tabaci ( Gennadius) Biotype B (= B. argentifolii Bellows & Perring) in cotton using chemical insecticides. Identical experimental designs and data collection protocols were used at sites in Brawley. CA. Yuma and Maricopa, AZ, and Weslaco, TX. The prescriptive application of insecticides based on 4 candidate action threshold levels (2.5, 5, 10, or 20 adult B. tabaci per leaf) were compared with one another and an untreated control. In general, there were few differences in whitefly populations among action thresholds of 2.5, 5, and 10 adults per leaf at sites in Arizona and California. All insecticide treatments typically reduced population densities below those in untreated control plots. Insecticide applications were generally ineffective in Weslaco, possibly due to reduced insecticide susceptibility or the late onset of pest infestation, and there were few differences in population density among treatments. Yields were higher in sprayed treatments, but there was little difference among threshold levels. Yield differences were not detected among any treatments for Yuma and Weslaco in 1994 and for Maricopa in 1995. The levels of lint stickiness due to honeydew deposition, as measured by thermodetector, were not consistent among sites and were not generally related to pest densities in the different threshold treatments. Levels of stickiness tended to be higher in 1994. There were no treatment effects on other standard measures of lint quality. A simple budgeting analysis assuming $43.24/ha per application for insecticides and $1.59/kg for lint suggested that action thresholds of 5-10 adults per leaf provided the highest net return at most sites.